In recent years, active researches have been conducted on dual-band portable telephones using two communication systems for one terminal in order to ensure a sufficient number of communication channels. Since a dual-band portable telephone uses two frequency bands, it requires two of each of the following components that are normally required in a high frequency block: low noise amplifier (Low Noise Amplifier; hereinafter referred to as “LNA”); power amplifier (Power Amplifier; hereinafter referred to as “PA”); down-mixer (Down Mixer; hereinafter referred to as “D-Mix”); up-mixer (up Mixer; hereinafter referred to as “U-Mix”); and local signal generator (voltage Controlled Oscillator; hereinafter referred to as “VCO”), and it also requires a power switch for operating these components in a time division manner, a reception path switch (hereinafter referred to as “RX-SW”) for switching the reception path, a transmission path switch (hereinafter referred to as “TX-SW”) for switching the transmission path, etc.
FIG. 32 illustrates an example of a high frequency block of a conventional dual-band portable telephone. In FIG. 32, 101 denotes an antenna (hereinafter referred to as “ANT”), 102 denotes a 1-input/4-output antenna switch (hereinafter referred to as “ANT-SW”), 111 denotes an LNA1, 112 denotes an LNA2, 121 denotes a D-Mix1, 122 denotes a D-Mix2, 131 denotes a U-Mix1, 132 denotes a U-Mix2, 141 denotes a PA1, 142 denotes a PA2, 151 denotes a VC01, 152 denotes a VC02, 161 denotes an RX-SW, and 162 denotes a TX-SW.
The operation of the high frequency block illustrated in FIG. 32 will now be described briefly.
The ANT 101 catches radio wave in the air and guides it into the telephone. The ANT-SW 102 connects one of the four signal paths RX1, RX2, TX1 and TX2 to the ANT 101.
Next, the operation of the reception side will be described. The following description will be made with respect to the signal path RX1 for example. A signal having a frequency fRX1 that is received at the ANT 101 is amplified by the LNA1 111 and passed to the D-Mix1 121. The VC01 151 generates a signal having a frequency fLO1, and fRX1 and fLO1 are mixed together at the D-Mix1 121, thus being down-converted to a frequency fIF. At this time, the absolute value of fRX1–fLO1 is fIF. The operation of the LNA2 112 and the D-Mix2 122 in the signal path RX2 is just as described above, wherein a frequency fRX2 received at the ANT 101 and a frequency fL02 generated by the VC02 152 are mixed together at the D-Mix2 122, thus being down-converted to the frequency fIF. At this time, the absolute value of fRX2–fLO2 is fIF. While the RX-SW 161 switches between signals from the D-Mix1 121 and the D-Mix2 122, the subsequent circuit components after the RX-SW 161 can be shared because the frequencies of the output terminals of the D-Mixes are both fIF.
Next, the operation of the transmission side will be described. The following description will be made with respect to the signal path TX1 for example. While the TX-SW 162 is switched so as to input a signal to either one of the U-Mix1 131 and the U-Mix2 132, the frequency of the signal is fMOD in either case. The VC01 151 generates a signal having the frequency fLO1, and the signals having the frequencies fMOD and fLO1 are mixed together at the U-Mix1 131, thus being up-converted to a frequency fTX1. At this time, the sum of fLO1 and fMOD is fTX1. The PA1 141 amplifies the signal having the frequency fTX1 from the U-Mix1 131 to the antenna transmission output. The operation of the U-Mix2 132 and the PA2 142 in the signal path TX2 is just as described above, wherein the sum of fLO2 and fMOD is fTX2.
Now, the configuration of the LNA block of the dual-band portable telephone will be described in detail with particular focus on the LNA block in FIG. 32.
FIG. 33 illustrates an example of an LNA block of a conventional dual-band portable telephone. 10 denotes a power supply, 1111 denotes an input terminal of the LNA1 111, 1121 denotes an input terminal of the LNA2 112, 1112 denotes an output terminal of the LNA1 111, 1122 denotes an output terminal of the LNA2 112, 1114 denotes a power supply SW of the LNA1 111, 1124 denotes a power supply SW of the LNA2 112. In FIG. 33, the peripheral matching components, etc., are omitted, and each area surrounded by a broken line denotes an individual device. This also applies to other drawings discussed below.
The power supply SW of the LNA1 1114 is connected between a power supply terminal of the LNA1 111 and the power supply 10, and turns on/off the power supply of the LNA1 111. The power supply SW of the LNA2 1124 is connected between a power supply terminal of the LNA2 112, and turns on/off the power supply of the LNA2 112. The respective ground terminals of the LNA1 111 and the LNA2 112 are both connected to the ground.
In a portable telephone, it is important to reduce the power consumption thereof in order to ensure a long calling time. Therefore, the power supply of a device that is not being operated is typically turned off. Specifically, when the LNA1 111 is operated, the power supply of the LNA2 112 is turned off. Therefore the power supply SW 1114 is turned on and the power supply SW 1124 is turned off. Conversely, when the LNA2 112 is operated, the power supply of the LNA1 111 is turned off. Therefore, the power supply SW 1124 is turned on and the power supply SW 1114 is turned off. Moreover, during transmission, neither the LNA1 111 nor the LNA2 112 needs to be turned on. Therefore, both of the power supply SWs 1114 and 1124 are turned off.
Typically, a 3- to 4-terminal device such as a transistor or a regulator is used as a power supply SW, and a 3- to 4-terminal device such as an Si bipolar transistor or a GaAs FET is used as an LNA. Therefore, the LNA block as a whole requires a total of 4 devices, i.e., two 3- to 4-terminal devices as power supply SWs and two 3- to 4-terminal devices as LNAS. Moreover, this directly applies to the other three blocks, i.e., PA, D-Mix and U-Mix, as well as the LNA block, and a total of four devices, i.e., two power supply SWs and two amplification devices such as transistors are required for each block.
Thus, when producing a dual-band portable telephone using a conventional device, it requires twice as many components as those for a single-band portable telephone. As a result, the mounting area on the substrate increases, whereby it is difficult to reduce the size of the terminal.
An object of the present invention is to reduce the number of components in a high frequency block of a dual-band portable telephone so as to realize a reduction in the size of the dual-band portable telephone.